Some power banks will shut off the power if the device (i.e. Teensy) doesn't draw enough power. Paul had posted a circuit years ago for this problem. I discovered this device on crowdsupply, that I bought, but I haven't used yes...
I created a spreadsheet for my own use that attempts to list the pin compatibility between the Teensy 3.x/LC/4.x versions (note, Teensy 3.0 is in the table, but the columns are hidden to reduce the size of the table)...